1. Field of the Invention
The present invention relates to an inkjet recording apparatus having a unit configured to heat a recording medium for the fixation of ink on the downstream side of a recording portion.
2. Description of the Related Art
Recent inkjet recording apparatuses in the field of sign and display can handle coated paper, uncoated paper, cloth, vinyl chloride materials, and polyester materials as recording media, and can perform recording on a wide variety of materials. The inkjet recording apparatuses are used for various indoor and outdoor applications, such as outdoor signs, indoor graphics, and vehicle wrapping. In such inkjet recording apparatuses, high accuracy in image quality, high definition, and high-speed printing are required as well as water resistance and weather resistance.
This field is characterized in that ink is put on a recording medium and fixed by heating. A unit configured to heat a recording medium using a heating unit such as a heater to promote the fixation of ink is known. As a heating unit, a configuration provided with a preheater for preheating a recording medium before recording and an afterheater drying the recording medium after recording has been proposed (see International Publication No. 04/094150).
It is known that because recording media used in this field are expanded by heat, a corrugation in the conveying direction is formed in the image forming region. This corrugation leads to a decrease in image quality.
Corrugations formed in a recording medium in the image forming region include a corrugation caused by the soaking of ink into the recording medium and the swelling of the recording medium, and a corrugation caused by the expansion of the recording medium due to the heating for the fixation of ink.
As a countermeasure against the corrugation caused by the soaking of ink into the recording medium and the swelling of the recording medium, a configuration is known in which ribs at a constant pitch are disposed from the image forming region to a downstream portion in the recording medium conveying direction, and spurs are disposed in the downstream portion (see Japanese Patent Laid-Open No. 2004-106978). This evenly disperses the corrugation formed in the recording medium that continues to swell even after recording. In the recording region, the expansion of the recording medium is dispersed as a corrugation fitting into the gaps between the ribs, and the recording medium is prevented from grazing the recording head.
Corrugations formed by heating include a corrugation that is formed in the image forming region by the heating in the image forming region, and a corrugation that is formed in a fixation promoting region downstream of the image forming region by the heating in the fixation promoting region and that spreads to the image forming region.
A method for reducing the corrugation formed by heating a recording medium in the image forming region is known that includes sucking the reverse side of the recording medium through a flat platen surface.
As a countermeasure against the corrugation in a recording medium in a printer, Japanese Patent Laid-Open No. 7-178993 is known although this is in the field of thermal-transfer printers. According to this, the corrugation can be spread out by a convex roller located downstream of the image forming region. Thus, the corrugation in the image forming region can be removed.
In an inkjet recording apparatus that heats a recording medium in a fixation promoting region on the downstream side of the image forming region, the progression of evaporation of ink and the decrease in the amount of heat removed as heat of vaporization in the fixation promoting region promote the temperature rise of the recording medium. Because the amount of expansion of the recording medium increases with temperature, the recording medium expands significantly in the fixation promoting region, and one or several ridges are formed and spread to the recording region.
In the configuration of Japanese Patent Laid-Open No. 7-178993, the recording medium needs to be conveyed a predetermined distance in order to spread out the corrugation. Even if the corrugation formed in the image forming region can be regulated using a suction mechanism, the corrugation formed downstream of the image forming region when the roller is stopped cannot be removed. This decreases the image quality.